Nuclear power plant cables are mainly used in nuclear reactor buildings, nuclear auxiliary buildings and steam turbine buildings. Generally, pipelines or cable ducts are used to lay the cables, which are required to have reliable service life, thermal stability, moisture resistance, chemical stability and radiation resistance.
In order to ensure the high reliability of the system design and avoid the serious economic consequences caused by equipment damage, repeated multi-channel independent line systems and devices are usually adopted. Usually, two sets of independent line systems are used for power cables and three sets of independent line systems are used for control cables.
Common types of cables for nuclear power plants are: 6/10kV and 0.6/1kV power cables, 0.6/1kV control cables, 300/500V instrument cables and 300/500V compensation cables.
The following table is the specification table of a domestic company:
Table 11E Class nuclear power plant cable model name
Model name
1E class K3 power cable for YJYK3 copper core crosslinked polyethylene insulated halogen-free low smoke polyolefin sheathed nuclear power plant
YJY23K3 copper conductor crosslinked polyethylene insulated steel tape armored halogen-free low smoke polyolefin sheathed nuclear power plant class 1E K3 power cables
Copper core crosslinked polyethylene insulated halogen-free low smoke flame retardant thermosetable sheath nuclear power plant 1E class K1 power cables
YJYJ23K1 Copper core crosslinked polyethylene insulated steel tape armored halogen-free low smoke flame retardant thermosetable sheathed nuclear power plant class 1E K1 power cables
KYJYK3 copper core crosslinked polyethylene insulated halogen-free low smoke polyolefin sheathed nuclear power plant 1E Class K3 control signal cables
KYJY23K3 copper conductor crosslinked polyethylene insulated steel tape armored halogen-free low smoke polyolefin sheathed nuclear power plant class 1E K3 control signal cables
Copper core, crosslinked polyethylene insulated, halogen-free, low smoke, flame retardant, thermosetable sheathed nuclear power plant, K1 control signal cables of class 1E
Copper core crosslinked polyethylene insulated steel tape armored halogen-free, low smoke, flame retardant thermosetable sheath nuclear power plant class 1E K1 control signal cable
Class 1E cables used in nuclear power plants are divided into three categories according to the safety categories of nuclear power plant electrical system equipment: K1, K2 and K3.
Safety categories K1, K2 and K3 are defined as follows:
Class K1 electric actuator.
Installed within the containment of a nuclear reactor and capable of performing its prescribed functions under normal environmental conditions and under SL2 (safe shutdown earthquake) loads and during or after an accident.
K2 class electric actuator.
Installed within the containment of a nuclear reactor and capable of performing its prescribed functions under normal environmental conditions and under SL2 (safe shutdown earthquake) loads.
Class K3 electric actuators.
Installed outside the containment of a nuclear reactor, it performs its prescribed functions under normal environmental conditions and under SL2 (safe shutdown earthquake) loads.
The operating environment of the three types of cables is very different, among which the K1 class has the most severe operating environment and the most stringent performance requirements on the cables. Only by simulating the coolant Loss accident (LOCA) test can the cables be put into operation.
According to the actual operating environment of the cable, both the inside and outside of ContainmentVessel will be severely tested when LOCA occurs in nuclear power plant.
Some people think that the cable installed in the nuclear reactor building should be simulated LOCA test;
Secondly, only by being able to produce class 1E K1 cables can it be proved that the cable manufacturer is fully capable of producing nuclear grade cables. It is best to determine the structural design and performance indicators of the cables according to the specific conditions of the two operating environments of the reactor building and the nuclear auxiliary building.
1. Test contents
(1) Type test of basic performance of cable;
(2) Cables shall be able to pass the vertical combustion test of bundle-formed cables specified in EEE383;
(3) Smoke concentration test;
(4) Gas release test of finished cable sheath material during combustion;
(5) Electric aging test of power cables;
(6) Long-term heat resistance assessment test for insulation and sheath materials;
(7) Thermal aging simulation test equivalent to 50 years of operation;
(8) Equivalent radiation aging simulation test running for 50 years;
(9) Simulated seismic test;
(10) Equivalent 50-year LOCA radiation exposure test, LOCA simulation test (high temperature, high pressure water vapor);
(11) Performance inspection test.
Among them, (1)~(3) are type tests, (7)~(10) are environmental simulation tests, and (8) and (10) are both conducted after the 7th test.
The performance inspection tests include voltage test, combustion test, measurement of tensile strength of insulation and sheath, elongation at break, etc.
The specific conditions of the operating environment are determined.
2. Test method
A. Electric aging test for power cables at 5000h
The power cables shall pass the electrical aging test for 5000h, which shall be conducted in accordance with lEC60502.
Test conditions are as follows:
(1) Length of cable sample: no less than 30m;
(2) Voltage applied: Voltage applied between phases (is the rated power-frequency voltage between the cable conductors);
(3) Apply the current: The current should pass through the cable to make the conductor temperature reach 95~100℃;
(4) Duration of a cycle: heating for 8h, then cooling for 16h;
(5) The test duration shall not be less than 5000h (namely 209 temperature cycles).
Test results: The cable should not be broken during the test.
The test voltage and test time are determined on the basis of the cable insulation life index (N) with a certain safety margin. The electrical aging life equation is: Unt=C[(1), U is the voltage applied on the cable; n is the life index; T is the electrical breakdown time; C is a constant (related to structure, etc.)].
If the life index of the crosslinked polyethylene used is N ≥9, the cable life of the nuclear power plant is required to be 50 years. Equation (1) can be used to calculate the voltage and time relationship.
For example, if the working voltage U=10kV, the required working time t=348000h(50 years);
When the test voltage is 20kV, the test time is required to be 5000h.
By substituting the above parameters into Equation (1), it can be obtained that:
The solution can be obtained as n=6.45, less than 9, indicating that the test method has a safety margin.
B. Evaluation test for long-term heat resistance of insulation and sheath materials
According to the IEC60216 standard and IEEE383-74 standard, the recommended mathematical model for accelerating the aging of nonmetal materials is Arrhenius' empirical formula :In =ab/T (2), refers to the working life of the product In temperature T (h);
T is the operating temperature (K);
A and B are undetermined coefficients.
Formula (2) has been applied for decades, and it is verified to be effective in many cases.
The undetermined coefficients A and B can be calculated based on the set working temperature, and then use formula (2) to calculate the life span. If the value of is greater than the expected one, the design life requirements will be satisfied.
(1) Determination of test temperature and time.
The conventional aging test is 135℃ and 168h, so 135℃ can be determined as the minimum test temperature.
Test protocols refer to IEC60216" to determine the thermal aging test procedures and!
General procedure for evaluating test results "and IEEE383 standard.
Life evaluation test temperature difference of each level is 15℃, there are four test temperature points, the maximum test temperature is 180℃.
The experiment lasted for about 5000h.
(2) Selection of life termination parameters.
In the thermal aging process of insulation materials, there are two characteristic parameters, namely tensile strength and elongation at break. In this test, the rate of decline of elongation at break is faster than that of tensile strength, so the elongation at break is taken as the life evaluation parameter.
According to the calculation of bending radius of cable laying, the actual elongation of insulation shall not exceed 10%.
The original elongation at break of the sample measured was 160%. Assuming that the retention rate of elongation at break was 50% as the life end point, the elongation at break was still 80%, which provided sufficient safety factor for the cable in operation.
(3) Data processing and life calculation.
According to IEC60216-1 and related mathematical principles, the Arrhenius curve was first drawn with the drawing method according to the assumed end-of-life point.
At the same time, undetermined coefficients A and B are calculated to determine the relationship between temperature and life of the test material. When the calculated life value is not less than 50 years at 90℃, the material is judged to have a qualified life of 50 years.
C. Thermal aging simulation test equivalent to 50 years of operation
According to THE IEEE383-74 standard, the thermal aging simulation test of finished cable samples was carried out by placing the cable in an air circulation oven at a certain temperature and time using the data developed by Arrhenius technology.
The thermal characteristics of insulation and sheath materials shall be based on the thermal life assessment results.
The Arrhenius curve and the relationship between temperature and life of the established materials with a service life of 50 years were used as the basis for determining the simulation test data of cable aging of finished products.
The Arrhenius curve and the relationship between temperature and life have been established, which are assumed to be the point before the end of life when the material's elongation at break retention rate is 50%. The thermal aging simulation test for finished cable samples equivalent to 50 years should be conducted at 90 ° C.
In the Arrhenius curve, a new curve and the relationship between temperature and time are established according to Equation (2) and the known slope to select the temperature and time of the simulation test.
D. Equivalent radiation aging simulation test running for 50 years
The finished cable samples for radiation tests should undergo thermal aging simulation tests equivalent to 50 years of operation.
The equivalent radiation aging simulation test operated for 50 years takes C60 as the radioactive source, and the radiation rate is no more than 1.0×104Gy/h and the radiation dose is 2.5×105Gy, which meets the radiation resistance performance requirements of the cable under the normal radiation dose environmental conditions in the nuclear auxiliary plant and reactor plant.
E. Simulated seismic tests
The cable sample is wound around the test cylinder with a diameter of 20D(D is the outside diameter of the cable) for at least one turn, and then the process is repeated in the opposite direction for one cycle, a total of two cycles.
After the winding cycle, the sample wound on the cylinder was put into an oven heated to the rated operating temperature of the cable for 24h. After cooling, the specified performance inspection test was carried out.
F. the equivalent
Radiation exposure tests during 50 years of OPERATION of LOCA, simulated LOCA tests (exposure under high temperature and high pressure water vapor)
LOCA(Lossofcoolantaccident) is also known as a water loss accident in light water reactors.
Coolant loss accidents sometimes occur in boiling water reactor (BWR) or pressurized water reactor (PWR) systems due to pipe leakage or other causes.
In this case, the cables, both inside and outside the containment vessel, are subjected to varying degrees of heat and pressure, chemical sprays, and historically high doses of gamma radiation.
Only cables tested through this simulated LOCA condition can be safely used in nuclear power plants.
Therefore, the CABling in the reactor building, both inside and outside the containment, should be LOCA tested.
G. Performance inspection test
The performance inspection tests include compressive tests, combustion tests, tests of insulation resistance, tensile strength of insulation and sheath, and tests of elongation at break. The tests of insulation resistance, tensile strength and elongation at break are for reference only.
Withstand voltage test: bend the sample with a bending diameter 40 times that of the cable diameter in the sample, and then apply the voltage with a gradient of 3.15kV/min for 5min. The cable should not break down.